The invention relates to a locking device for telescoping legs of furniture items such as tables or chairs, which are adjustable in height.
Adjustable telescoping legs are used in particular in office chairs. Usually, the outer leg is in the form of an upright tube, connected at its lower end with support means, such as for example, arms diverging in the shape of a star, while the inner telescoping tube is connected with the seating surface or, in the case of tables, with the table top. The inner telescoping tube slides in the outer telescope tube, so that adjustment in height is possible.
To secure the seating or working position desired, it is necessary to immobilize the inner telescope tube in a certain vertical position in relation to the outer telescope tube. Locking devices of varied designs are used for that purpose. Following the release of such a device, the inner telescope tube and thus the seat or working plate slides downward by gravity and must then be manually adjusted to the desired height. The height selected is then immobilized by the actuation of the locking device. In more advanced designs, additionally a load compensation means in the form, for example of a spring (such as a helical spring or a gas spring) is provided, which applies an upwardly directed force longitudinally to the inner telescoping tube. The magnitude of the force of this spring may be such that the inner telescoping tube is always moving in the upward direction, when the locking device is released. This configuration is especially preferred in office chairs. The correct seating position is then attained by loading the seating surface and locking it at the correct height, but the force of the spring acting on the inner telescoping tube may also be such that it just compensates for the weight of the seating or working surface. It is then possible to adjust the height without the use of any appreciable force. A spring setting of this type is used in particular with greater weights of the seating or working surface, preferably with tables.
Different configurations for the mutual immobilization of the position of the telescoping legs have already been proposed. For example, German DE-OS No. 26 07 144 proposes to apply a corrugation over a certain area of the outer tube. Projections of a clamping sleeve engage the beads of the corrugated tube, the sleeve being expanded by a conical inner telescoping tube. By sliding the clamping sleeve along the cone, the projections may be released from the beads so that an adjustment in height becomes possible. The sliding of the clamping device is effected by an adjusting rod under spring pressure extending axially within the inner telescoping tube, the rod being, in turn, actuated by an elbowed lever.
With a height adjusting device of this type, no continuous height adjustment is possible, as the projections of the clamping sleeve permit locking only if they are abutting against the corresponding beads of the outer corrugated tube. The corrugation of the outer tube further results in an unfavorable aesthetic appearance.
Another locking device of the afore-mentioned type is described in German DE-OS No. 24 06 338. There, a rod-shaped or tubular body is provided in the inner tube, which at its lower end terminates in a cone. A plurality of radial bores is provided at the lower end of the inner pipe in which balls are located. The cone of the cylindrical body presses these balls against the outer tube. The immobilization obtained in this manner may be released by axial movements of the cylindrical body or of the inner telescope tube, whereby the balls slide along the surface of the cone.
Adjusting devices of this type are structurally expensive in view of the additional cylindrical body and the balls used, including their bearings. Furthermore, the frictional joint by means of balls may be exposed to limited loads in one direction only, which is especially disadvantageous, if for example, a table top is being pressured upwards by a spring, resulting in stresses in both directions. This adjusting device may thus be applied only to layouts without spring powered load compensations, for example, a simple chair. It is not applicable to an arrangement with load compensation.
It is an object of the present invention to eliminate the disadvantages of the known configurations and to provide a locking device that is mechanically simple, may be loaded heavily, and permits continuous height adjustments.